The present invention relates to a laser apparatus of the waveform control type and a laser monitor apparatus for use therewith.
A pulsed laser beam processing apparatus employs a method to variably control a laser power waveform of a pulsed laser beam in order to meet various processing requirements. In accordance with the waveform control method, a desired reference waveform of laser power is preset into the laser beam processing apparatus. In the laser beam processing apparatus, a laser electric power supply which supplies electric power to a laser oscillator is controlled by an open-loop control or a closed-loop control so that the power of the laser beam oscillated from the laser oscillator can follow the reference waveform.
A laser monitor apparatus for monitoring laser power, which is incorporated in a laser beam processing apparatus or has the form of an independent unit electrically connected thereto, has been used for the sake of quality control in a laser beam processing site.
In the prior art laser monitor apparatus, a part of a laser beam is projected on a photo detector such as photo-diode which produces an electric signal (a laser detection signal) corresponding to the laser power or intensity of light of the laser beam. The signal is integrated to obtain a measured value of laser energy (Joule) per unit time or one pulse. Judging how far apart the measured laser energy value is from a predetermined reference value or whether the measured value is within the limit of a predetermined monitoring value or not, the laser monitor apparatus outputs decision on whether the laser beam processing has been performed normally or not, or whether the resulting quality of processing is good or not.
However, such laser monitor apparatus has not worked effectively in the above type of laser apparatus using waveform control method. In the waveform control method, it is important how closely an actual laser power waveform follows a reference waveform. The prior art laser monitor apparatus makes a decision of good or bad on the quality of processing on the basis of a measured value (mean value) of laser energy per unit time or one pulse. Therefore, even if the actual laser power waveform deviates so far apart from the reference waveform as to influence the quality of processing, the laser monitor apparatus may determine the processing to be normal, failing to determine it to be defective, as long as the total laser energy or the average laser energy of the whole pulse is within the allowable range.